diff --git a/Engine.cc b/Engine.cc
index 0aa2eea..997bf64 100644
--- a/Engine.cc
+++ b/Engine.cc
@@ -96,6 +96,7 @@ Engine::Engine(const string & path, Video & video)
     : m_video(video)
 {
     m_next_object_index = 1;
+    m_next_joint_index = 1;
     m_next_text_index = 1;
     m_eye[0] = 0;
     m_eye[1] = -1;
@@ -306,7 +307,9 @@ int Engine::addAMotor(Object * o1, Object * o2)
     if (o2 != NULL)
         b2 = o2->getBody();
     dJointID j = dJointCreateAMotor(m_world.getWorldID(), 0);
-    /* TODO: finish */
+    int id = m_next_joint_index++;
+    m_joints[id] = j;
+    return id;
 }
 
 void Engine::removeObject(int id)
diff --git a/Engine.h b/Engine.h
index d7c329b..781d5de 100644
--- a/Engine.h
+++ b/Engine.h
@@ -213,6 +213,7 @@ class Engine
         std::map<int, Object *> m_objects;
         std::map<int, dJointID> m_joints;
         int             m_next_object_index;
+        int             m_next_joint_index;
         int             m_next_text_index;
         GLdouble        m_eye[3];
         GLdouble        m_center[3];